1. Field of the Invention
The present invention relates to the field of integrated circuit, and more particularly to a CMOS offset trimming circuit and an offset generation circuit using the same.
2. Background of the Invention
Generally, offset is more frequently generated in the CMOS analog circuit than in the bipolar circuit because of the factors such as a mismatch, a change of Vt, and a body effect in the MOS transistor. It is an inevitable phenomenon in view of the characteristics of the CMOS process and the characteristics of the MOS transistor. But, the best way for realizing a precise analog circuit is to minimize the generation of the offset by an appropriate correction.
In case that the trimming is effected by cutting a metal line, it is important to obtain an optimum offset correction value before the cutting of the metal line, since the metal line can not be restored to its original state. In the present invention, the optimum offset correction value can be obtained by changing the value of the offset within a permitted correction range. And, the trimming is performed using the optimum offset value. Thus, the offset of the CMOS analog circuit can be minimized.
According to the prior art, it is impossible to obtain an optimum correction value for minimizing the offset. And, the number of pins required for the correction is increased in proportion to the offset correction range in case that a wide range of offset correction is needed. Further, the cost for manufacturing the integrated circuit is high due to an additive process required for the trimming.
When the analog circuit is realized as an integrated circuit, it is necessary to perform the trimming after the manufacturing process thereof. In particular, it is on an increasing trend to embody the analog integrated circuit by CMOS rather than by bipolar. In view of the real situation as above, the need of the trimming technique for the offset correction is greatly emphasized. But, there is no circuit by which the optimum offset value can be obtained in the prior art, so that it is impossible to perform the trimming using the optimum value for minimizing the offset according to the prior art.